Gas Turbine Handbook : Principles and Practices

Boroscope Inspection 205
Chapter 13
Boroscope Inspection
OBJECTIVES AND EXPECTATIONS
When used in conjunction with gas path, vibration, and trending
analysis techniques, boroscope inspections often provide
the final step in the process of identifying an internal problem.
However, it would be misleading to think that periodic boroscope
inspections could be a substitute for the other analysis techniques.
Boroscope inspections are useful in providing a general view of the
condition of critical components, but they are limited by the gas turbine
design, boroscope design, and capability of the inspector.
The problems discussed in this chapter, and the photographs
used, are taken from actual gas turbines. All gas turbines have, at
one time or another, experienced these or similar problems. Therefore,
the reader is cautioned not to conclude that a particular problem
is associated only with a specific gas turbine model or manufacturer.
To insure that this treatise remains as generic as possible, the photographs
will be identified as to engine component position and nominal
gas turbine power output and not to manufacturer or model number
(although readers well acquainted with particular models will readily
recognize them from the photographs).
Boroscope inspections are visual examinations subject to the
experience of the individual and the quality of the instrument being
used. Before undertaking a boroscope inspection, the inspector needs
to determine the suitable diameter and length of the boroscope for
use in each boroscope port. Also the intensity of the boroscope light
source must be determined for each location to be inspected. Depending
on the skill and experience of the inspector, one boroscope, properly
selected, will satisfy all of the necessary requirements. Where
access to the viewed object is achieved through a straight path, the
rigid boroscope (Figure 13-1) is a useful tool. This is especially true
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